Foliose lichen. Lichen on a tree twig. This species is classified as foliose, due to its leafy appearance. Lichens are organisms formed by the symbiotic association of a fungus and an alga or cyanobacterium. The algal cells use photosynthesis to produce nutrients which are absorbed by fungal hyphae that surround and penetrate the algae. Fungal hyphae also absorb minerals from rainwater or acidic digestion of the substrate. Lichen reproduce both sexually, through the formation of fungal spores, or asexually, through production of soredia. Magnification: x8 when printed 10 centimetres wide.